This invention relates to marking an article with an invisible marking for security or validation purposes and particularly, to marking a digital recording medium. More particularly, the invention relates to placing a marking on a compact disk (CD) using an invisible fluorescing compound. The invention also relates to a method of applying and detecting the fluorescing compound.
In the field of recording medium and recordings thereon, the recent use of digitally recorded information, such as pictures, sounds, software and the like using what is generally known as a compact disk or disc, has greatly improved the quality of the recording, the durability of the recording, and lowered the cost relative to prior magnetic storage tapes and disks. The production of the recorded information is accomplished by a process which, rather simplistically, may be described as an injected molded thermoplastic process. The recorded material on the CD is a series of data bits represented as pits and landings which are converted by the reading instrument, such as a CD player, to reproduce the recording. In one method of producing a CD, the information from the premastering data is recorded optically onto the surface of a glass master disk or substrate coated with a photoresist. From the glass master, a stamper is produced by depositing a nickel layer onto the glass master using an electroforming process. The stamper is then used to thermomold the CD in a replication process. Once thermoformed, the transparent CD is coated with an aluminum layer using a process known as metalizing. The CD is then coated with a protective lacquer to protect the reflective aluminum surface. The good CD is then mounted on a spindle. The whole process takes less than about 15 seconds. Using a screen printing process and methods known to those skilled in the art, the non-recorded surface of the CD can display graphics, art or other printed information. After printing, the CDS are automatically packaged into a hinged, clear plastic box, known as a jewel box, and wrapped in a clear plastic. The jewel box may contain further printed information on the inside or its cover.
Although the CD has revolutionized the recording industry, it is not without its problems. Because of the relative ease of manufacture, CD recordings can be readily counterfeited, depriving the recording artists, producers and distributors of income for their work. It is desirable in many commercial fields to provide a means by which an object may be identified as an original or authenticated or to prevent forgery or counterfeiting. In the past, previously used methods utilized ultraviolet inks or paints that fluoresce when subjected to an ultraviolet light source. Such markings produce a dramatic effect, since the markings, which originally seem invisible in visible or normal light, become visible when exposed to ultraviolet radiation. Examples of printing variable information such as bar codes with an ink jet printer utilizing the invisible markings are described in U.S. Pat. Nos. 5,423,432; 4,540,595; 5,093,147 and 4,983,817 the entire disclosures of which are incorporated herein by reference. However, the fundamental problem with such markings is that they can be easily located by a counterfeiter or product diverter. Moreover, such markings are highly susceptible to other fluorescent dyes and optical brighteners which are readily available on the market today.
U.S. Pat. No. 3,614,430 issued to Berler on Oct. 19, 1971 discloses a method for electronically retrieving coded information imprinted on a substantially translucent substrate. The ink used to code the information fluoresces when exposed to ultraviolet light. The fluorescence is photoelectrically sensed through the translucent substrate. A reader device then interprets the coded information and may further preform a desired output relative to the coded information.
U.S. Pat. No. 3,933,094 issued to Murphy et al. on Jan. 20, 1976 discloses a substrate such as, a business reply envelope, having bar code information imprinted thereon. The bar code is printed on the substrate using a plurality of inks having a color which, in combination with the substrate, yields a Print Contrast Signal substantially less than 50 percent when measured in the wavelength range of 800 to 900 nanometers. Added to the ink is a metallic compound sufficient to increase the Print Contrast Signal of the ink and substrate to at least 50 percent.
U.S. Pat. No. 4,504,084 issued to Miehe et al. on Nov. 12, 1991 discloses a method for marking originals so that copies can be distinguished from the originals. The method includes using a ribbon having a printing medium for printing the original. The ribbon includes a substance in the form of a marking which, when used, produces an invisible distinguishable marking which is recognizable only by using a special scanner.
U.S. Pat. 5,461,136 discloses polyesters having certain infrared fluorophores copolymerized therein to provide invisibly marked or tagged polymeric composition and a method of detection.
However, marking CDS or any of the packaging components has not been previously disclosed.
Accordingly, there is a need for a means by which a CD may be marked and identified as being an original.